This invention relates to methods of making manganese sulfide. In particular, the present invention relates to methods of making manganese sulfide using iron pyrite as a reaction moderating material.
Manganese sulfides occur routinely when making steel. Sulfur is present in many of the raw materials to make steel and manganese has long been one of the most common and inexpensive alloying elements used in steelmaking. During melting and refining, the sulfur present in the molten raw materials selectively combines with manganese to form manganese sulfides (MnS). In addition to preventing sulfur from causing a hot short condition in the iron matrix during hot working, the discrete manganese sulfide particles (commonly referred to as inclusions) also serve as chip breakers during subsequent machining operations. These natural breaks in the chips generated during a machining operation reduce tool wear, and allow better control of the machining and a better surface finish on the final part.
Many metallurgical powders used to fabricate powder metal parts are made from pure elemental powders, such as iron, manganese and chrome. When using powders that do not contain sulfur, no inclusions are formed. Therefore, machining the metal parts made from powders without sulfur is difficult and expensive. The addition of pure sulfur powder is not a solution to this difficulty because sulfur powders are potentially both safety and environmental hazards. In addition, sulfur powder may not react, or completely react, to form MnS.
Thus, the value of metallurgical powders can be greatly enhanced by introducing an engineered MnS powder to control the size and distribution of MnS inclusions. This approach led to the desire to produce MnS with controlled chemical properties having specific particle sizes to maximize the benefits of MnS inclusions while minimizing other undesirable properties.
As an additive in powder metallurgy techniques (PM), manganese sulfide enhances performance and machinability of metal articles made by PM processes. Improved machinability is desired where metal part designs have increasingly complex geometry features and surface textures.
Current demand for manganese sulfide cannot be met by mining techniques because an insufficient amount of manganese sulfide exists in the earth""s crust. The metallurgical industry has therefore turned to artificial means of producing manganese sulfide.
Traditional methods of synthesizing manganese sulfide have undesirable properties, such as for example, producing high concentrations of impurities, creating sulfur pollution, and producing low yields at high costs. For example, manganese sulfide can be synthesized with submerged arc furnaces that utilize manganese containing ores and sulfur bearing materials. Manganese sulfide is also produced by precipitating manganese sulfide from an aqueous solution of manganese salt and alkaline sulfide. Another technique thermally reduces manganese sulfate with carbon or hydrogen to form manganese sulfide. These techniques produce large quantities of environmentally hazardous vaporized sulfur and the manganese sulfide products produced therefrom have high impurity concentrations.
Techniques that yield small quantities of manganese sulfide are undesirable such as for example those techniques that recycle a portion of manganese sulfide product from one reaction to a second reaction. Conventional techniques recycle between about 15% to about 40% of the final manganese sulfide product of one reaction to control the reaction parameters of a subsequent reaction.
Other conventional methods of producing manganese sulfide are known and described in U.S. Pat. Nos. 4,676,970 and 5,768,678 which are herein incorporated by reference. The 970 patent describes a method for making a fused compound wherein a product is recycled during the reaction. The 678 patent describes a metal sulfide composition for use as a machining aid.
The metallurgical industry is in search of reliable, low cost, environmentally friendly methods of making commercial quantities of high purity manganese sulfide. Methods that address these needs have long been sought.